Methods and apparatus for encoding and decoding a downlink control channel transmission

ABSTRACT

Methods and apparatus for encoding and decoding a downlink control channel transmission, such as but not exclusively a High Speed Signalling Control Channel, HS-SCCH, transmission, in a wireless communications network. A method in a network node for encoding a downlink control channel transmission, comprises determining that channel conditions are below a threshold level, and in response to determining that channel conditions are below the threshold level, performing at least one of: encoding one or more predetermined control information bits into the downlink control channel transmission, and encoding a reduced number of control information bits into the downlink control channel transmission by omitting one or more control information bits, wherein the one or more omitted control information bits are predetermined control information bits. The method further comprises transmitting the downlink control channel transmission to a user equipment. A method in a user equipment for decoding a downlink control channel transmission, comprises receiving the downlink control channel transmission, and decoding the downlink control channel transmission based on knowledge of the predetermined control information bits.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/326,245, filed Feb. 18, 2019, which was the National Stage ofInternational Application No. PCT/EP2016/069750, filed Aug. 19, 2016,each of which is incorporated by reference in its entirety.

FIELD

The present invention relates to methods and apparatus for encoding anddecoding a downlink control channel transmission, such as but notexclusively a High Speed Signalling Control Channel, HS-SCCH,transmission, in a wireless communications network.

BACKGROUND

The HS-SCCH is a fixed rate (60 kbps, SF=128) downlink physical channelused to carry control information related to a HS-DSCH (High SpeedDownlink Shared Channel) transmission. A HS-DSCH conveys data to betransmitted in the downlink. The HS-SCCH is specified in 3GPP TS 2.211“Physical channels and mapping of transport channels onto physicalchannels (FDD)” version 13.0.0, release 13.

A HS-SCCH type 1 contains the following fields:

Structure of the HS-SCCH Type1 (Control Information fields):

-   -   Channelization-code-set information (7 bits): x_(ccs,1),        x_(ccs,2), . . . , x_(ccs,7)    -   Modulation scheme information (1 bit): x_(ms,1)    -   Transport-block size information (6 bits): x_(tbs,1), x_(tbs,2),        . . . , x_(tbs,6)    -   Hybrid-ARQ process information (3 bits): x_(hap,1), x_(hap,2), .        . . , x_(hap,3)    -   Redundancy and constellation version (3 bits): x_(rv,1),        x^(rv,2), x_(rv,3)    -   New data indicator (1 bit): x_(nd,1)    -   UE identity (16 bits): x_(ue,1), x_(ue,2), . . . , x_(ue,16)

FIG. 1 illustrates the Layer 1, L1, processing chain for a HS-SCCH type1 transmission, as specified in 3GPP TS 25.212 “Multiplexing and channelcoding (FDD)” version 13.0.0, release 13.

The HS-SCCH control information is transmitted in one subframe, which iscomposed of three slots: slot 0 (known as a HS-SCCH part 1), and slots 1and 2 (known as a HS-SCCH part 2). Both the “Channelization-code-setinformation” (bits x_(ccs)) and the “Modulation scheme information” (bitx_(ms)) are transmitted in slot 0 (i.e. in HS-SCCH part 1), while the“Transport-block size information” (bits x_(tbs)), “Hybrid-ARQ processinformation” (bits x_(hap)) Redundancy and constellation version” (bitsx_(rv)), and the “New data indicator” (bit x_(nd)) are conveyed overslot 1 and slot 2 (i.e. in HS-SCCH part 2). The “UE identity” (bitsx_(ue)) is masked in both HS-SCCH part 1 and part 2, as shown in FIG. 1.

The branch inputting to the “UE specific masking” 40 in the left handprocessing chain of FIG. 1 (which encodes the channelization code setinformation and modulation scheme information into HS-SCCH part 1) isnot explicitly shown in the standard. This branch shows an encodingprocess of the “UE identity” into the HS-SCCH part 1. This process usesChannel Coding of “coding rate 1/2” 42 and rate matching 44corresponding to “Rate matching 1” 30 in the processing chain located inthe center of FIG. 1 (left hand processing chain as depicted in thestandard). On the other hand, the “UE identity” is masked into part 2 ofthe HS-SCCH with a CRC calculated from X₁ and X₂ shown FIG. 1 . The CRCis then attached to the Transport-block size information, Hybrid-ARQprocess information, Redundancy and constellation version and the Newdata indicator in HS-SCCH part 2 60 as shown in the right handprocessing chain of FIG. 1 .

The lengths of the bit sequences at each stage of the respectiveprocessing chains have been indicated in FIG. 1 . In respect of the lefthand processing chain multiplexing, “mux” 10 of the“Channelization-code-set information” (bits x_(ccs)) and the “Modulationscheme information” (bit x_(ms)) produces X₁ 8 bits. “Channel Coding 1”of 1/3 20 (zero-tailed) is then applied, which produces Z₁ 48 bits.“Rate matching 1” 30 then reduces the number of bits to R₁ 40 bits,which after being masked with an encoded version of the UE Identity (40bits), are fitted into slot 0 of a HS-SCCH subframe (as shown next tothe “Physical channel mapping” step 90). Similarly, in the right handprocessing chain the bits “Transport-block size information” (bitsx_(tbs)), “Hybrid-ARQ process information” (bits x_(hap)), Redundancyand constellation version” (bits x_(rv)), and the “New data indicator”(bit x_(nd)) are multiplexed at 50 to produce X₂ 13 bits. After the “UEspecific CRC attachment” there is Y 29 bits. “Channel coding 2” 70 isthen applied, which produces Z₂ 111 bits. “Rate matching 2” 80 thenreduces the number of bits to R₂ 80 bits, which fit into slot 1 and slot2 of a HS-SCCH subframe (again as shown next to the “Physical channelmapping” step 90).

At a User Equipment, UE, which receives a HS-SCCH transmission, theHS-SCCH is detected/decoded in two stages: The HS-SCCH part 1 (slot 0)is detected/decoded first. This detection/decoding needs to beconsidered as “passed” before a UE can proceed to decode the HS-SCCHpart 2 (slot 1 & 2). Thus, the detection/decoding of a HS-SCCH slot 0 isa key aspect of the performance of the HS-SCCH.

The applicant has appreciated that a problem in relation to performanceis that the HS-SCCH is costly in terms of downlink, DL, power, inparticular in poor radio conditions.

SUMMARY

According to an aspect of the present invention, there is provided amethod in a network node for encoding a downlink control channeltransmission. The method comprises determining that channel conditionsare below a threshold level, and, in response to determining thatchannel conditions are below the threshold level, performing at leastone of: encoding one or more predetermined control information bits intothe downlink control channel transmission, and encoding a reduced numberof control information bits into the downlink control channeltransmission by omitting one or more control information bits, whereinthe one or more omitted control information bits are predeterminedcontrol information bits. The method further comprises transmitting thedownlink control channel transmission to a user equipment.

According to a further aspect of the present invention there is provideda method in a user equipment for decoding a downlink control channeltransmission. The method comprises receiving a downlink control channeltransmission from a network node, wherein the downlink control channeltransmission carries one or more predetermined control information bitsor omits one or more predetermined control information bits such thatthe downlink control channel transmission carries a reduced number ofcontrol information bits. The method further comprises decoding thedownlink control channel transmission based on knowledge of thepredetermined control information bits.

The present invention has the advantage that it enables an improvementin decoding performance of a downlink control channel at a UE inparticular in poor radio conditions. For example, the decodingperformance may be improved in terms of BLER (Block Error Rate), “missdetection” and/or “false detection”. This is because by fixing one ormore of the control information bits, and the UE decoding a downlinkcontrol channel transmission based on knowledge of these one or morefixed or predetermined control channel information bits, a reduction indecoding complexity may be achieved at the UE. Thus, the presentinvention, advantageously, enables power savings in the downlink, DL, inparticular in poor radio conditions. For example, according toembodiments of the present invention, a downlink control channeltransmission having a reduced Eb/No (bit energy to noise spectraldensity) ratio may achieve the same performance as a legacy downlinkcontrol channel transmission having a higher Eb/No ratio. Networkcoverage may also therefore be advantageously maintained or improvedwithout increasing DL power.

In a first embodiment, the method at the network node may compriseencoding one or more predetermined control information bits into thedownlink control channel transmission. This embodiment has the advantagethat the method may be back-compatible for use with legacy UEs. That is,legacy UEs may still be able to decode the downlink control channelcarrying the one or more predetermined control information bits (whichmay be referred to as a “Low cost” downlink control channel). However,the legacy UEs will not benefit from any decoding performanceimprovement, since they are not configured to make use of knowledge ofthe one or more predetermined control information bits.

In a second embodiment, the method at the network node may compriseencoding a reduced number of control information bits into the downlinkcontrol channel transmission by omitting one or more control informationbits, wherein the one or more omitted control information bits arepredetermined control information bits. In this embodiment, encoding thereduced number of control information bits into the downlink controlchannel transmission may comprise applying rate matching, for exampleusing a puncturing pattern, in dependence on the total number of the oneor more omitted control information bits.

In a first embodiment, when the downlink control channel transmissioncarries one or more predetermined control information bits, the methodat the UE may comprise decoding the downlink control channeltransmission based on knowledge of the predetermined control informationbits by using a predetermined subset of a set of codewords for use indetermining a portion of the downlink control channel transmission todecode the portion of the downlink control channel transmission. In thisway, the number of possible hypothesis (i.e. codewords) which need to betested by the UE against the received sequence of control informationbits is reduced. Thus decoding complexity may be reduced.

In a second embodiment, when the downlink control channel transmissionomits one or more predetermined control information bits such that thedownlink control channel transmission carries a reduced number ofcontrol information bits, the decoding at the UE may comprise applyingrate matching, for example using a puncturing pattern, in dependence onthe total number of the one or more omitted control information bits.

In some embodiments, determining at the network node that channelconditions are below a threshold level may comprises receiving a ChannelQuality Indicator, CQI, from the user equipment and using the ChannelQuality Indicator, CQI, to determine that channel conditions are belowthe threshold level.

In some embodiments, the method at the UE may comprise sending a ChannelQuality Indicator, CQI, to the network node.

In a preferred embodiment, the method at the UE may further comprisedetermining that channel conditions are below a threshold level, and, inresponse to determining that channel conditions are below a thresholdlevel, decoding the downlink control channel transmission based onknowledge of the predetermined control information bits. This mayfurther reduce decoding complexity, since the UE may only for exampleuse the predetermined subset of codewords to decode the downlink controlchannel transmission if channel conditions are below a threshold leveland so the UE is expecting a “low cost” downlink control channeltransmission. However, in other embodiments there may be no such triggerat the UE, and the UE may for example simply attempt to decode eachreceived downlink control channel transmission using knowledge of thepredetermined control information bits and, then only if this fails,proceed to decode the received downlink control channel transmission inthe usual manner. Or, vice versa the UE may only attempt to decode areceived downlink control channel transmission using knowledge of thepredetermined control information bits, if normal decoding has failed.

In some embodiments, determining at the UE that channel conditions arebelow a threshold level may comprise using information reported to thenetwork node in a Channel Quality Indicator, CQI, to determine thatchannel conditions are below the threshold level. This may facilitatecoordination between the network node and the UE.

The downlink control channel transmission may be a High Speed SignallingControl Channel, HS-SCCH transmission. However, it should be appreciatedthat the invention may be applied to other suitable downlink controlchannel transmissions.

In particular, when the downlink control channel transmission is aHS-SCCH, the one or more predetermined control information bits mayinclude one or more channelization-code-set information and modulationscheme information bits. Thus, the one or more predetermined controlinformation bits may relate to part 1 of a HS-SCCH. In this case, the“portion” of the downlink control channel referred to above may be part1 of a High Speed Signalling Control Channel, HS-SCCH. This has theadvantage that the decoding performance of part 1 of a HS-SCCH may beimproved, which is a key improvement as part 2 of a HS-SCCH is onlydecoded if part 1 is deemed to be successfully decoded, as explainedabove.

However, in other embodiments of the present invention, the one or morepredetermined control information bits may alternatively, or inaddition, be carried in part 2 of a HS-SCCH. That is, the one or morepredetermined control information bits may include one or moretransport-block size information, Hybrid-ARQ process information,Redundancy and constellation version and New data indicator bits. Wherethe one or more predetermined control information bits are part of part2 of a HS-SCCH, the second embodiment where a reduced number of controlinformation bits are encoded into the downlink control channeltransmission by omitting one or more predetermined control informationbits may be particularly advantageous. This is because, owing to thegreater number of bits transmitted in the HS-SCCH part 2 in comparisonto the HS-SCCH part 1, reducing the number of bits may better facilitatea reduction in decoding complexity for HS-SCCH part 2, as will beexplained in more detail below.

There is further provided a network node configured (i.e. operative) toperform any of the methods described above.

There is further provided a user equipment configured (i.e. operative)to perform any of the method described above.

There is further provided a computer program comprising computerreadable instructions which, when performed on a processor, may performany of the methods described above. There is further provided a computerreadable medium comprising the computer program.

DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 illustrates the Layer 1, L1, processing chain for a HS-SCCH type1 transmission;

FIG. 2 illustrates a method at a network node according to anembodiments of the present invention;

FIG. 3 illustrates a method at a user equipment according to anembodiments of the present invention;

FIG. 4 illustrates a method according to preferred embodiments of thepresent invention;

FIGS. 5 a, 5 b, and 5 c illustrate, by way of example only, a legacychannelization code set, a reduced channelization code set (one codeonly) and a reduced channelization code set (two codes only),respectively;

FIG. 6 illustrates an example predetermined subset of a set of codewordsfor use in decoding part 1 of a HS-SCCH transmission;

FIG. 7 is a graph showing misdetection performance for a legacy HS-SCCHtype 1 versus an example “Low cost” HS-SCCH type 1 (slot 0);

FIG. 8 is a graph showing false detection performance for a legacyHS-SCCH type 1 versus an example “Low cost” HS-SCCH type 1 (slot 0);

FIG. 9 is a graph showing Block Error Rate, BLER, performance for alegacy HS-SCCH type 1 versus an example “Low cost” HS-SCCH type 1 (slot0);

FIG. 10 illustrates a network node according to an embodiment of thepresent invention;

FIG. 11 illustrates a user equipment according to an embodiment of thepresent invention;

FIG. 12 illustrates a network node according to a further embodiment ofthe present invention; and

FIG. 13 illustrates a user equipment according to a further embodimentof the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide methods and apparatus forencoding and decoding a downlink control channel transmission, such asbut not exclusively a High Speed Signalling Control Channel, HS-SCCH,transmission, in a wireless communications network. The wirelesscommunications network may be a UMTS (Universal MobileTelecommunications System) mobile cellular system. However, embodimentsof the present invention may be used in other types of wirelesscommunications networks, such as by way of example only other 2G/3Gnetworks, LTE (Long-Term Evolution), LTE Advanced or 5G. As indicatedabove, the downlink control channel transmission may be a HS-SCCHtransmission. However, the downlink control channel transmission couldalternatively be any other type of downlink control channeltransmission.

FIG. 2 illustrates a method at a network node for encoding a downlinkcontrol channel transmission according to embodiments of the presentinvention. The network node may also be referred to as a radio networknode, and may for example be a radio access network node such as a basestation, for example a node B, or a base station operating incoordination with a base station controller.

The method comprises at 200 determining that channel conditions arebelow a threshold level. This may be done by monitoring channelconditions, for example by monitoring a parameter indicative of ameasure of channel conditions, and comparing the monitored channelconditions to a threshold. The threshold may be predetermined.Alternatively, the network node could for example receive an indication,for example from another network node, that channel conditions are orare expected to be below a threshold level, from which the network nodecan “determine” that channel conditions are below a threshold level.

The method further comprises, in response to determining that channelconditions are below the threshold level, either at 205 encoding one ormore predetermined control information bits into the downlink controlchannel transmission, or at 210 encoding a reduced number of controlinformation bits into the downlink control channel transmission byomitting one or more control information bits, wherein the one or moreomitted control information bits are predetermined control informationbits. It may be noted that by virtue of encoding one or morepredetermined control information bits into the downlink control channeltransmission, the control information which can be conveyed by thedownlink control channel transmission is limited. However, the applicanthas appreciated that this may be an acceptable trade-off/limitation, inparticular in poor radio conditions where certain modes of operation mayin any case not be practical. For example, as will be explained below,in poor radio conditions there may be limitations on the “Number ofcodes” and the “Modulation scheme” that can be used in a downlink datachannel (e.g., HS-PDSCH) associated with the downlink control channel(e.g. HS-SCCH).

Where a reduced number of control information bits are encoded into thedownlink control channel transmission, encoding 210 may compriseapplying 212 rate matching, for example using a puncturing pattern, independence on the total number of the one or more omitted controlinformation bits. Thus, in this way, although fewer control informationbits are encoded into and thus carried by the downlink control channeltransmission, the number of bits actually transmitted in the downlinkcontrol channel transmission may remain the same as if the omittedcontrol information bits were included in the downlink control channeltransmission. Thus, no modifications to the physical layermapping/transmission of the downlink control channel transmission may berequired.

The method further comprises at 220 transmitting the downlink controlchannel transmission to a user equipment (UE).

FIG. 3 illustrates a method at a user equipment for decoding a downlinkcontrol channel transmission according to embodiments of the presentinvention. The user equipment can be any type of wireless device capableof communicating with a network node or another UE over radio signals/anair interface. The user equipment may, for example but not exclusively,be a radio communication device, a target device, a D2D(device-to-device) UE, a UE capable of machine to machine typecommunication, a sensor equipped with a UE, a personal digitalassistant, PDA, a tablet, a mobile terminal, a smart phone, a laptopembedded equipment, LEE, a laptop mounted equipment, LE, a USB dongle,Customer Premises Equipment, CPE.

The method at the user equipment comprises at 310 receiving a downlinkcontrol channel transmission from a network node, wherein the downlinkcontrol channel transmission carries one or more predetermined controlinformation bits or omits one or more predetermined control informationbits such that the downlink control channel transmission carries areduced number of control information bits. The method further comprisesat 320 decoding the downlink control channel transmission (e.g.determining a sequence of control information bits encodedin/transmitted over the downlink control channel transmission) based onknowledge of the one or more predetermined control information bits. Forexample, the decoding may be based on knowledge of which one or morecontrol information bits in the downlink control channel transmissionare predetermined (or fixed) and their value (i.e. a “O” or a “1”).

By using knowledge of the one or more predetermined control informationbits, the decoding complexity at the user equipment may be reduced.

As will be understood by those skilled in the art different types ofdecoder may be used at a user equipment. For example, the user equipmentmay use a “Sequential Maximum Likelihood Correlator” to decode at leasta portion of a downlink control channel transmission. Such a decoder maycompare the received control information bits with all possiblecodewords and select for example the codeword providing a sufficientlyhigh correlation to pass a predefined threshold as the codewordrepresented by the control information bits. However, the user equipmentcould alternatively use another type of decoder. For example, the userequipment could use a “Viterbi decoder”, which as will be understood bythose skilled in the art instead traces simultaneously differentpossible paths across a Trellis diagram and selects the path having thebest metric as the result. Other types of decoder are possible and willoccur to those skilled in the art.

In one embodiment, the downlink control channel transmission carries anumber of predetermined control information bits (i.e. the total numberof control information bits received by the user equipment on thedownlink control channel transmission may be the same as if the downlinkcontrol channel transmission were a legacy transmission). In this case,the method at the user equipment may comprise at 322 using apredetermined subset of a set of codewords for use in decoding a portionof the downlink control channel transmission to decode the portion ofthe downlink control channel transmission. That is, only a predeterminedsubset of codewords obtained from the full set of codewords may be usedwhen determining the sequence of information bits that was transmittedover the portion of the downlink control channel. The subset ofcodewords need only include those permutations possible taking intoaccount that a certain one or ones of the control information bits arefixed. Thus, in some embodiments, this may result in the user equipmentneeding to test significantly fewer codewords against the receivedcontrol information bits—and thus a corresponding reduction in decodingcomplexity. However, other ways of decoding a downlink control channeltransmission leveraging on knowledge that the downlink control channeltransmission carries one or more predetermined control information bits,and so reducing decoding complexity/improving decoding performance, mayoccur to those skilled in the art.

It should be noted that the “portion” of the downlink control channeltransmission mentioned above may comprise only a part of the downlinkcontrol channel transmission. For example, as will be explained below,the portion may comprise only part 1 of a HS-SCCH. However, in someembodiments, the “portion” of the downlink control channel transmissioncould comprise the entire downlink control channel transmission.

The predetermined subset of the set of codewords may for example bestored in a memory at the user equipment. Thus using the predeterminedsubset of the set of codewords as indicated above may compriseretrieving the subset of the set of codewords from a memory at the userequipment.

As indicated above, the downlink control channel transmission may be aHS-SCCH.

FIGS. 5 a, 5 b, and 5 c and 6 illustrate an example implementation ofthe present invention in relation to a HS-SCCH. In this example, the oneor more predetermined control information bits comprise one or morechannelization code set information and modulation scheme informationbits. Thus, the one or more predetermined control information bits arein the “channelization code set information” field and/or the“modulation scheme information” field in part 1 of a HS-SCCH (i.e.transmitted in slot 0 of a HS-SCCH type 1).

FIGS. 5 a, 5 b, and 5 c illustrate, by way of example only, aChannelization Code Set showing codes which may be included in the“channelization code set information” field, a reduced ChannelizationCode Set (one code only) and a reduced Channelization Code Set (twocodes only) respectively.

As mentioned above, the Channelization Code Set (CCS) informationconsists of seven bits. More particularly, the CCS information is splitinto two parts: The first part refers to a “Code Group Indicator” whichconsists of 3 bits from X_(ccs1) to X_(ccs3). The second part refers toa “Code Offset Indicator” which consists of 4 bits, X_(ccs4) from toX_(ccs7). The binary sequence mapped to the CCS bits depends on thevariables “P” and “O”, which respectively refer to the number of codesused by the downlink transmission and the offset (i.e., the position ofthe codes) in the channelization code tree. An example of the relationbetween the CCS bits and the variables “P” and “O” is shown in FIG. 5 a.

In the example shown in FIG. 5 a , the network node, for example a NodeB, has determined that the number of codes of a downlink transmission tobe transmitted is five (P=5), while the offset in the channelizationcode tree is seven (O=7). Upon knowing the value of “P” and “O”, the CCSbits are determined as follows:X _(ccs1) ,X _(ccs2) ,X _(ccs3)=min(P−1,15−P)=100.X _(ccs4) ,X _(ccs5) ,X _(ccs6) ,X _(ccs7) =|O−1−(Floor(P/8))(15)|=0110.

Thus, the CCS bits X_(ccs1), . . . X_(ccs7)=1000110.

The CCS bits contain the “coordinates” that allow the UE to find thevalue of “P” and “O” within the “Channelization Code Set matrix”depicted in FIG. 5 a.

On the other hand, the Modulation Scheme (MS) bit is used to inform theUE whether the modulation scheme applied on the HS-PDSCH is QPSK or16-QAM. The interpretation is as follows:x _(ms,1)=0→QPSKx _(ms,1)=1→16-QAM.

In this example, a so called “Low Cost HS-SSCH Type 1” or simplifiedHS-SCCH, which comprises a number of predetermined control informationbits, is intended to be utilized by UEs that at most can make use ofQPSK with 1 code.

In that case, the “Code Group Indicator” (3 bits) is not needed anymore,and neither is the “Modulation Scheme” bit. Therefore, the HS-SCCH partI can be limited to indicate only the “Code Offset Indicator” fieldconsisting of 4 bits as depicted in FIG. 5 b.

Thus, for this simplified version of a HS-SCCH type 1, “P” would befixed to 1, keeping X_(ccs4), X_(ccs5), X_(ccs6),X_(ccs7)=|O−1−(Floor(P/8))(15)|.

Note the combination X_(ccs4), X_(ccs5), X_(ccs6), X_(ccs7)=1111 isunused and would remain available for other applications/purposes (e.g.,for retransmissions purposes, or instructing the UE to perform aspecific action).

On the hand, if using one code only were considered too restrictive,then using two codes may be considered. In that case, the “Code GroupIndicator” would consist of 1 bit, in addition to the 4 bits of the CodeOffset Indicator as depicted in FIG. 5 c . For this simplified versionof the HS-SCCH type 1, “P” can take the value of 1 or 2, keepingX_(ccs4),X_(ccs5),X_(ccs6)X_(ccs7)=|O−1−(Floor(P/8))(15)|. When “P”=1,the combination X_(ccs4), X_(ccs5), X_(ccs6), X_(ccs7)=1111 is unusedand would remain available for other applications/purposes (e.g., forretransmissions purposes, or instructing the UE to perform a specificaction). When “P”=2, the combinations X_(ccs4), X_(ccs5), X_(ccs6),X_(ccs7)=1111 and 1110 are unused and would remain available for otherapplications/purposes (e.g., for retransmissions purposes, orinstructing the UE to perform a specific action).

Thus, for example, where the “Low Cost HS-SCCH type 1” uses only onechannelization code, and QPSK modulation, only four bits among all thecontrol information bits carried on the slot 0 (HS-SCCH part 1) are notdeterministic. These are the bits used for indicating the Offset in thechannelization code tree (i.e., the code position in the channelizationcode tree).

The mapping of the control information bits carried on the slot 0 of the“Low Cost HS-SCCH Type 1” may therefore be as follows:

-   -   x_(ccs,1), x_(ccs,2), x_(ccs,3)=000: Following the legacy        format, this bit sequence indicates that only one code is used.    -   x_(ccs,4), x_(ccs,5), x_(ccs,6), x_(ccs,7)=0000→1110: Following        the legacy format, the range for the offset goes from 0 to 14        (meaning offset 1 to 15), since one code is reserved for common        channels. In other words, only fifteen out of the sixteen codes        are usable code positions.    -   x_(ms,1)=0: Following the legacy format, this means the QPSK        modulation is used.

The above means that for the CCS+MS 8-bit sequence, half of the bits aremade deterministic i.e. are predetermined:

-   -   x_(ccs,1), x_(ccs,2), x_(ccs,3), x_(ccs,4), x_(ccs,5),        x_(ccs,6), x_(ccs,7), x_(ms,1)=000????0

Therefore, in this example, when the “Low Cost HS-SCCH type 1” is inuse, there are only fifteen possible control information bit sequencesthat can be transmitted in the HS-SCCH part 1. These possible bitsequences (i.e. codewords) are shown in FIG. 6 .

These possible bit sequences thus represent an example predetermining asubset of a set of codewords for use in decoding part 1 of a HS-SCCHtransmission according to an embodiment of the present invention. At theUE, this means that the decoding complexity of the HS-SCCH part 1 may bereduced (i.e., fewer hypothesis need to be tested) since the unmaskedcontrol information bit sequence needs to be correlated only against inthis example 15 codewords instead of against approximately 256 codewordsas for a legacy HS-SCCH part 1 transmission where none of the 8 controlinformation bits are predetermined. This enables an improvement in theBLER (Block Error Rate), False Detection and Miss Detection performance.

For illustrative purposes a simulation has been run using a particularsetup (targeting 1% BLER and a false detection rate below 10%) for botha legacy HS-SCCH and this example “Low Cost HS-SCCH”. The MissDetection, False Detection, and BLER performance for the legacy and the“Low Cost HS-SCCH” (slot 0, i.e. part 1) is shown in FIGS. 7, 8 and 9respectively.

In the graph of FIG. 7 it is seen that the percentage of Miss Detectionsdrops as a function of the Eb/No ratio for both the legacy HS-SCCH andthe example “Low Cost HS-SCCH”. However, the percentage of MissDetections drops faster when the “Low Cost HS-SCCH” is utilized, andoverall the percentage of Miss Detections is lower for a “Low CostHS-SCCH”. It should be noted that the number of “Miss Detections”impacts the BLER, since in this analysis a transmission that was missedby the UE was counted as a block error.

FIG. 8 is a graph showing the percentage of False Detections versusEb/No for a legacy HS-SCCH and the example “low cost HSCCH”. It is seenthat the percentage of False Detections is substantially the same fordifferent Eb/No ratios for both the legacy HS-SCCH and the example “lowcost HS-SCCH”. However, it is seen that the percentage of falsedetection is reduced, almost by half, when the “Low Cost HS-SCCH” isused.

FIG. 9 is a graph showing BLER versus Eb/No again for a legacy HS-SCCHversus the example “low cost HS-SCCH”. An acceptable BLER target for theHS-SCCH is around 1% (i.e., 10⁻² in the plot depicted in FIG. 9 ). Atthat operation point the “low cost HS-SCCH” provides a gain that isaround 1.3 dB with respect to the legacy performance.

In the above example, it should be noted that advantageously the “Lowcost HS-SCCH” is compatible with legacy UEs, since the predeterminedcontrol information bits have been fixed according to a legacy sequencewith the desired meaning, i.e. “1 code, QPSK”. Thus, a legacy UE wouldstill be able to decode the “Low cost HS-SCCH”. However, the legacy UEswill not take advantage of the predetermined control information bits.

Further, in the above example, one or more control information bits in aHS-SCCH part 1 are predetermined. However, according to some examples,one or more control information bits in a HS-SCCH part 2 may in additionor alternatively be predetermined according to embodiments of thepresent invention.

For example, fixing the number of codes in the HS-SCCH part 1 restrictsthe content of the control information carried on the HS-SCCH part 2.For example, using only one code implies that the Transport-block sizeinformation (6 bits) will not use the full range of possible of“Transport Block” sizes, which opens the possibility of also fixing someof the transport block size information bits. In general, the “Low Cost”simplification strategy can be extended to some other controlinformation fields in the HS-SCCH part 2. For example, the Redundancyand constellation version (3 bits) bit sequence can be fixed too, if forexample it is predetermined that either “Chase Combining” or“Incremental Redundancy” will be used when the “Low Cost HS-SCCH” isenabled.

In the above example, the one or more predetermined control informationbits are carried in the downlink control channel transmission, and thusreceived by the UE. However, alternatively as explained above, the oneor more predetermined control information bits may be omitted from thedownlink control channel transmission. Referring back to FIG. 3 , inthis case, at 324, decoding the downlink control channel transmissionmay comprise applying rate matching for example using a puncturingpattern in dependence on the total number of the one or more omittedcontrol information bits. This rate matching may therefore correspond tothe rate matching used at the network node in relation to encoding thedownlink control channel transmission. Thus, the UE may be able torecover the reduced number of control information bits. Since the UEthen only needs to be able to decode fewer control information bits,decoding complexity may be reduced. In addition, this may advantageouslybe achieved without any or substantial modification to the decoder atthe UE, for example if the decoder is a Viterbi decoder.

The Applicant has appreciated that this alternative method for reducingdecoding complexity may be suitable for the HS-SCCH part 2 for example.Note that, since the HS-SCCH part 1 and HS-SCCH part 2 are decodedseparately, different decoding methods may be used for the two parts.The HS-SCCH part 2 is transmitted over two slots and carries a largernumber of control information bits than the HS-SCCH part 1: 13 bits+16bits CRC which results in 536870912 (i.e. 2{circumflex over ( )}29)codewords (in comparison to 256 for the HS-SCCH part 1). Even iftherefore say 6 bits out of the 29 bits are fixed, 8388608 codewordswould still need to be tested. Thus, in this case, making use of ageneric decoder such as a Viterbi decoder and omitting the predeterminedcontrol information bits may enable an improved decoding performance.For example, the Viterbi decoder may be able to search for the best pathin a shorter time.

Taking the HS-SCCH part 2 as an example, in the legacy format asexplained above with respect to FIG. 1 , 13 bits (X_(tbs), X_(hap),X_(rv), X_(nd)) 16 bits (UE_ID)+8 bits (Zero Tail)=37 bits. ChannelCoding 70 of a 1/3 CC(1/3) increases the number of bits to 111. Ratematching 80 then reduces the number of bits to 80. If for example six ofthe control information bits are predetermined—and removed—then instead7 bits (e.g. X_(hap), X_(rv), X_(nd)) 16 bits (UE_ID)+8bits(ZeroTail)=31 bits. CC(1/3) increases the number of bits to only 93.Thus rate matching is then required to reduce those 93 bits to 80 bits,to fit into slot 1 and 2 of the HS-SCCH. Thus, in the legacy format,rate matching discards 31 bits in order to provide an output of 80 bits.In the modified version, by way of example, rate matching insteaddiscards only 13 bits in order to provide an output of 80 bits. In thiscase, a corresponding rate matching, e.g. here puncturing 13 bits, needsto be performed at the UE to retrieve the transmitted controlinformation bits.

FIG. 4 illustrates a method for encoding and decoding a downlink controlchannel transmission according to preferred embodiments of the presentinvention. Steps which may be performed at a UE are shown on theleft-hand side of the page, and steps which may be performed at anetwork node are shown on the right-hand side of the page. It should benoted that at least some of the steps may be performed in a differentorder from that indicated in the flow diagram or simultaneously.

In this example, the network node determines that channel conditions arebelow a threshold level using information in a Channel QualityIndicator, CQI, reported by the UE. For example, if a CQI reports avalue below a predetermined threshold (indicative of poor radioconditions), the network node may determine that channel conditions arebelow a threshold level.

At 300, the UE sends a CQI to the network node. At 202 the network nodereceives the CQI from the user equipment and at 205 the network nodedetermines that channel conditions are below a threshold level using theCQI. In response to determining that channel conditions are below thethreshold level, the network node at 212 or 214, as explained above,encodes a number of predetermined control information bits into thedownlink control channel transmission, for example into one or morefields of the downlink control channel transmission. At 220, the networknode transmits the downlink control channel transmission to the UE. At310 the UE receives the downlink control channel transmission. The UEthen advantageously at 320 decodes the downlink control channeltransmission based on knowledge of the one or more predetermined controlinformation bits.

As indicated in FIG. 4 , prior to step 320, the UE may also at 302determine that channel conditions are below a threshold level. This maybe done using information reported in the CQI as indicated at 304. Thus,in response to the determination, the UE may expect a “low cost downlinkcontrol channel transmission” (i.e. a downlink control channeltransmission carrying or omitting the one or more predetermined controlinformation bits). Thus, in response to the determination, the UE maydecode the downlink control channel transmission based on knowledge ofthe one or more predetermined control information bits.

However, other embodiments are possible. For example, there may be adifferent or no such trigger at the UE. In the latter case, the UE mayfor example simply attempt to decode each received downlink controlchannel transmission using knowledge of the predetermined controlinformation bits and, then only if this fails, proceed to decode thereceived downlink control channel transmission in the usual manner. Or,vice versa the UE may only attempt to decode a received downlink controlchannel transmission using knowledge of the predetermined controlinformation bits, if normal decoding has failed.

A network node may be configured to perform any of the methods describedabove, for example with respect to FIGS. 2 and 4 .

FIGS. 10 and 12 illustrate a network node 1000, 1200 according toembodiments of the present invention. The network node may be any typeof network node that serves a UE and or is connected to another networknode or network element or any radio node from where a UE receives asignal. The network node may be a radio access network node, such as abase station (for example a node B) or a base station operating inco-ordination with a base station controller. In some examples thenetwork node may comprise a plurality of a distributed parts or networknodes.

The network node 1000 illustrated in FIG. 10 comprises transceivercircuitry 1010 and processing circuitry 1020. The transceiver circuitry1010 may include a transmitter circuit, a receiver circuit andassociated control circuits that are collectively configured to transmitand receive signals according to a radio access technology, for exampleaccording to a wireless communications standard such as GSM (GlobalSystem for Mobile Communications), GPRS (General Packet Radio Service),WCDMA (Wideband Code Division Multiple Access), LTE, LTE-Advanced, 5Getc. The processing circuitry 1020 may be operatively associated withthe transceiver circuitry 1010. The processing circuitry 1020 maycomprise one or more digital processors, for example one or moremicrocontrollers, digital signal processors, DSPs, field programmablegate arrays, FPGAs, complex programmable logic devices, CPLDs,application specific integrated circuits, ASIC or any combinationthereof. In general, the processing circuitry 1020 may comprise fixedcircuitry or programmable circuitry that is specially configured via theexecution of program instructions implementing functionality taughttherein, or include some combination of fixed and programmablecircuitry. The processing circuitry 1020 may also comprise a memory. Insome embodiments, the memory may store one or more computer programs andoptionally configuration data. The memory may comprise any type ofcomputer readable media, such as disk storage, solid state memorystorage or for example SRAM (Static Random Access Memory), DRAM (DynamicRandom Access Memory), EEPROM (Electrically Erasable ProgrammableRead-Only Memory) and flash memory.

The processing circuitry 1020 may be configured, via the transceivercircuitry 1010, to determine that channel conditions are below athreshold level, and, in response to determining that channel conditionsare below the threshold level, encode a number of predetermined controlinformation bits into one or more fields of the downlink control channeltransmission or encode a reduced number of control information bits intothe downlink control channel transmission by omitting one or morecontrol information bits, wherein the one or more omitted controlinformation bits are predetermined control information bits. Theprocessing circuitry 1020 may further be configured to transmit thedownlink control channel transmission to a user equipment.

In general, the processing circuitry 1020 may be configured to performany of the methods described above, for example described with respectto FIGS. 2 and 4 .

The processing circuitry 1020 may further be configured to, whenencoding the reduced number of control information bits into thedownlink control channel transmission, apply rate matching for exampleusing a puncturing pattern in dependence on the total number of the oneor more omitted control information bits.

In some embodiments, the processing circuitry 1020 may be configured todetermine that channel conditions are below a threshold level byreceiving a Channel Quality Indicator, CQI, from the user equipment andusing the Channel Quality Indicator, CQI, to determine that channelconditions are below the threshold level.

The downlink control channel transmission may be a High Speed SignallingControl Channel, HS-SCCH. The one or more predetermined controlinformation bits may include at least one or morechannelization-code-set information and the modulation schemeinformation bits.

FIG. 12 illustrates a network node 1200 according to a furtherembodiment of the present invention. In this embodiment, the networknode 1200 comprises a determining module 1210 for determining thatchannel conditions are below a threshold level. The network node 1200further comprises an encoding module 1220 for, in response todetermining that channel conditions are below the threshold level,encoding a number of predetermined control information bits into thedownlink control channel transmission or encode a reduced number ofcontrol information bits into the downlink control channel transmissionby omitting one or more control information bits, wherein the one ormore omitted control information bits are predetermined controlinformation bits. The network node 1200 further comprises a transmittingmodule 1230 for transmitting the downlink control channel transmissionto a user equipment.

When the downlink control channel transmission omits the one or morepredetermined control information bits, the encoding module 1220 may befor applying rate matching for example using a puncturing pattern independence on the total number of the one or more omitted controlinformation bits.

In some embodiments, the network node 1200 may further comprise areceiving module 1215 for receiving a Channel Quality Indicator, CQI,from the user equipment. In this case, the determining module 1210 maybe for determining that channel conditions are below a threshold levelusing the Channel Quality Indicator, CQI.

As indicated above, the downlink control channel transmission may be aHigh Speed Signalling Control Channel, HS-SCCH. The one or morepredetermined control information bits may include one or morechannelization-code-set information and the modulation schemeinformation bits.

The determining module 1210, encoding module 1220, transmitting module1230 and the receiving module 1215 may comprise any combination ofsoftware and or hardware, and may for example comprise transceivercircuitry and or processing circuitry as defined above. The modules1210, 1220, 1230 and 1215 may be integrated or distributed to anydegree.

Similarly, a user equipment, UE, may be configured to perform any of themethods described above, for example those described with respect toFIGS. 3 and 4 .

FIGS. 11 and 13 illustrates a user equipment 1100, 1300 according toembodiments of the present invention. The user equipment 1100, 1300 canbe any type of wireless device capable of communicating with a networknode or another UE over radio signals/an air interface. The userequipment 1100, 1300 may, for example but not exclusively, be a radiocommunication device, a target device, a D2D (device-to-device) UE, a UEcapable of machine to machine type communication, a sensor equipped witha UE, a personal digital assistant, PDA, a tablet, a mobile terminal, asmart phone, a laptop embedded equipment, LEE, a laptop mountedequipment, LE, a USB dongle, Customer Premises Equipment, CPE.

In the embodiment illustrated in FIG. 11 , the user equipment 1100comprises transceiver circuitry 1110 and processing circuitry 1120. Thetransceiver circuitry 1110 may include a transmitter circuit, a receivercircuit and associated control circuits that are collectively configuredto transmit and receive signals according to a radio access technology,for example according to a wireless communications standard such as GSM(Global System for Mobile Communications), GPRS (General Packet RadioService), WCDMA (Wideband Code Division Multiple Access), LTE,LTE-Advanced, 5G etc. The processing circuitry 1020 may be operativelyassociated with the transceiver circuitry 1010. The processing circuitry1020 may comprise one or more digital processors, for example one ormore microcontrollers, digital signal processors, DSPs, fieldprogrammable gate arrays, FPGAs, complex programmable logic devices,CPLDs, application specific integrated circuits, ASIC or any combinationthereof. In general, the processing circuitry 1120 may comprise fixedcircuitry or programmable circuitry that is specially configured via theexecution of program instructions implementing functionality taughttherein, or include some combination of fixed and programmablecircuitry. The processing circuitry 1020 may also comprise a memory. Insome embodiments, the memory may store one or more computer programs andoptionally configuration data. The memory may comprise any type ofcomputer readable media, such as disk storage, solid state memorystorage or for example SRAM (Static Random Access Memory), DRAM (DynamicRandom Access Memory), EEPROM (Electrically Erasable ProgrammableRead-Only Memory) and flash memory.

The processing circuitry 1110 is configured, via the transceivercircuitry 1110, to receive a downlink control channel transmission froma network node, wherein the downlink control channel transmissioncarries one or more predetermined control information bit or omits oneor more predetermined control information bits such that the downlinkcontrol channel transmission carries a reduced number of controlinformation bits. The processing circuitry 1110 is further configured todecode the downlink control channel transmission based on knowledge ofthe predetermined control information bits.

In general, the processing circuitry 1110 may be configured to performany of the methods described above, for example described with respectto FIGS. 3 and 5 .

When the downlink control channel transmission carries the one or morepredetermined control information bits, the processing circuitry 1110may be configured to use a predetermined subset of a set of codewordsfor use in determining a portion of the downlink control channeltransmission to decode the portion of the downlink control channeltransmission.

When the downlink control channel transmission omits the one or moredetermined control information bits, the processing circuitry 1110 maybe configured to decode the downlink control channel transmission basedon knowledge of the one or more predetermined control information bitsby applying rate matching for example using a puncturing pattern independence on the total number of the one or more omitted controlinformation bits.

In some embodiments, the processing circuitry 1110 may further beconfigured to send a Channel Quality Indicator, CQI, to the network node1000, 1200.

In some embodiments, the processing circuitry 1110 may further beconfigured to determine that channel conditions are below a thresholdlevel, and, in response to determining that channel conditions are belowa threshold level, decode the downlink control channel transmissionbased on knowledge of the one or more predetermined control informationbits.

The processing circuitry 1110 may be configured to determine thatchannel conditions are below a threshold level by using informationreported in the Channel Quality Indicator, CQI.

The downlink control channel transmission may be a High Speed SignallingControl Channel, HS-SCCH. The portion of the downlink control channelmentioned above may be part 1 of a High Speed Signalling ControlChannel, HS-SCCH.

FIG. 13 illustrates a user equipment 1300 according to a furtherembodiment of the present invention. The user equipment 1300 comprises areceiving module 1310 for receiving a downlink control channeltransmission from a network node, wherein the downlink control channeltransmission carries one or more predetermined control information bitsor omits a number of predetermined control information bits such thatthe downlink control channel transmission carries a reduced number ofcontrol information bits. The user equipment 1300 may further comprise adecoding module 1320 for decoding the downlink control channeltransmission based on knowledge of the predetermined control informationbits.

The decoding module 1320 may be for, when the downlink control channeltransmission carries one or more predetermined control information bits,using a predetermined subset of a set of codewords for use indetermining a portion of the downlink control channel transmission todecode the portion of the downlink control channel transmission. In anembodiment, the UE may comprise a retrieving module 1315 for retrievingthe predetermined subset of the set of codewords from a memory in theUser Equipment 1300.

The decoding module 1320 may be for, when the downlink control channeltransmission carries the reduced number of control information bits,applying rate matching for example using a puncturing pattern independence on the total number of the one or more omitted controlinformation bits.

The user equipment 1300 may further comprise a transmitting module 1312for sending a Channel Quality Indicator, CQI, to the network node.

In some embodiments, the user equipment 1300 may further comprise adetermining module 1314 for determining that channel conditions arebelow a threshold level. In this case, the decoding module 1320 may befor, in response to determining that channel conditions are below athreshold level, decoding the downlink control channel transmissionusing knowledge of the one or more predetermined control informationbits.

The determining module may be for determining that channel conditionsare below a threshold level by using information reported in the ChannelQuality Indicator, CQI.

The downlink control channel transmission may be a High Speed SignallingControl Channel, HS-SCCH. The portion of the downlink control channelreferred to above may be part 1 of a High Speed Signalling ControlChannel, HS-SCCH.

The receiving module 1310, decoding module 1320, transmitting module1312, retrieving module 1315 and determining module 1314 may compriseany combination of software and or hardware, and may for examplecomprise transceiver circuitry and or processing circuitry as definedabove. The modules 1310, 1320, 1330 and 1314 may be integrated ordistributed to any degree.

There may also be provided a computer program configured to, when run ona processor, perform any of the methods described above. The computerprogram may be stored on a non-transitory computer readable medium, suchas by way of example only disk storage, solid state memory storage orfor example SRAM (Static Random Access Memory), DRAM (Dynamic RandomAccess Memory), EEPROM (Electrically Erasable Programmable Read-OnlyMemory) and flash memory.

Thus, embodiments of the present invention have the advantage thatdecoding performance of a downlink control channel transmission may beimproved, for example in terms of one or more of BLER, miss detectionand false detection, in particular in poor radio conditions. Thus,advantageously, the downlink power required by the downlink controlchannel may be reduced, or maintained with a corresponding increase infor example network coverage. Furthermore, some embodiments, where theone or more predetermined control information bits are carried in thedownlink control channel transmission, may advantageously beback-compatible, whereby legacy UEs may still be able to decode thedownlink control channel transmission although they cannot benefit froman improvement in decoding performance.

The invention claimed is:
 1. A method in a network node for encoding adownlink control channel transmission to a user equipment, the methodcomprising: determining that channel conditions are below a thresholdlevel; in response to determining that channel conditions are below thethreshold level: encoding, into the downlink control channeltransmission, one or more predetermined control information bits whoseone or more respective values are known to the user equipment, orencoding a reduced number of control information bits into the downlinkcontrol channel transmission by omitting one or more control informationbits, wherein the one or more omitted control information bits are oneor more predetermined control information bits whose one or morerespective values are known to the user equipment; and transmitting thedownlink control channel transmission to the user equipment; wherein theone or more predetermined control information bits whose one or morerespective values are known to the user equipment are one or morecontrol information bits that the user equipment knows are to have theone or more respective values when channel conditions are below thethreshold level.
 2. The method according to claim 1, comprising, inresponse to determining that channel conditions are below the thresholdlevel, encoding into the downlink control channel transmission one ormore predetermined control information bits whose one or more respectivevalues are known to the user equipment.
 3. The method according to claim1, comprising, in response to determining that channel conditions arebelow the threshold level, encoding a reduced number of controlinformation bits into the downlink control channel transmission byomitting one or more control information bits, wherein the one or moreomitted control information bits are one or more predetermined controlinformation bits whose one or more respective values are known to theuser equipment.
 4. The method according to claim 3, wherein encoding thereduced number of control information bits into the downlink controlchannel transmission comprises applying rate matching in dependence on atotal number of the one or more omitted control information bits.
 5. Amethod in a user equipment for decoding a downlink control channeltransmission, comprising: receiving a downlink control channeltransmission from a network node, wherein the downlink control channeltransmission carries one or more predetermined control information bitsor omits one or more predetermined control information bits such thatthe downlink control channel transmission carries a reduced number ofcontrol information bits; determining that channel conditions are belowa threshold level; and in response to determining that channelconditions are below the threshold level, decoding the downlink controlchannel transmission based on knowledge that the one or morepredetermined control information bits are to have one or morerespective values when channel conditions are below the threshold level.6. The method according to claim 5, wherein the downlink control channeltransmission carries one or more predetermined control information bits.7. The method according to claim 6, wherein decoding the downlinkcontrol channel transmission based on knowledge that the one or morepredetermined control information bits are to have one or morerespective values when channel conditions are below the threshold levelcomprises decoding the downlink control channel transmission using apredetermined subset of a set of codewords.
 8. The method according toclaim 5, wherein the downlink control channel transmission omits one ormore predetermined control information bits such that the downlinkcontrol channel transmission carries a reduced number of controlinformation bits.
 9. A network node configured for use in encoding adownlink control channel transmission to a user equipment, the networknode comprising: transceiver circuitry; and processing circuitryconfigured to: determine that channel conditions are below a thresholdlevel; in response to determining that channel conditions are below thethreshold level: encode, into the downlink control channel transmission,one or more predetermined control information bits whose one or morerespective values are known to the user equipment, or encode a reducednumber of control information bits into the downlink control channeltransmission by omitting one or more control information bits, whereinthe one or more omitted control information bits are one or morepredetermined control information bits whose one or more respectivevalues are known to the user equipment; and transmit, via thetransceiver circuitry, the downlink control channel transmission to auser equipment; wherein the one or more predetermined controlinformation bits whose one or more respective values are known to theuser equipment are one or more control information bits that the userequipment knows are to have the one or more respective values whenchannel conditions are below the threshold level.
 10. The network nodeaccording to claim 9, wherein the processing circuitry is configured to,in response to determining that channel conditions are below thethreshold level, encode into the downlink control channel transmissionone or more predetermined control information bits whose one or morerespective values are known to the user equipment.
 11. The network nodeaccording to claim 9, wherein the processing circuitry is configured to,in response to determining that channel conditions are below thethreshold level, encode a reduced number of control information bitsinto the downlink control channel transmission by omitting one or morecontrol information bits, wherein the one or more omitted controlinformation bits are one or more predetermined control information bitswhose one or more respective values are known to the user equipment. 12.The network node according to claim 11, wherein the processing circuitryis configured to encode the reduced number of control information bitsinto the downlink control channel transmission by applying rate matchingin dependence on a total number of the one or more omitted controlinformation bits.
 13. The network node according to claim 11, whereincontrol information bits are encodable into the downlink control channeltransmission as any codeword from a set of possible codewords that eachhave the same number of control information bits, wherein said reducednumber of control information bits is less than said same number ofcontrol information bits, and wherein the processing circuitry isconfigured to encode, into the downlink control channel transmission,said same number of control information bits as a codeword from the setof possible codewords or said reduced number of control information bitsas a portion of a codeword from the set of possible codewords, dependingrespectively on whether channel conditions are above or below thethreshold level, wherein the portion of the codeword omits one or morecontrol information bits whose values are or are not predetermineddepending respectively on whether channel conditions are below or abovethe threshold level.
 14. The network node according to claim 9, whereinthe one or more predetermined control information bits comprise one ormore channelization-code-set information and modulation schemeinformation bits.
 15. A user equipment comprising: transceivercircuitry; and processing circuitry configured to: receive, via thetransceiver circuitry, a downlink control channel transmission from anetwork node, wherein the downlink control channel transmission carriesa number of predetermined control information bits or omits one or morepredetermined control information bits such that the downlink controlchannel transmission carries a reduced number of control informationbits; determine that channel conditions are below a threshold level; andin response to determining that channel conditions are below a thresholdlevel, decode the downlink control channel transmission based onknowledge that the one or more predetermined control information bitsare to have one or more respective values when channel conditions arebelow the threshold level.
 16. The user equipment according to claim 15,wherein the downlink control channel transmission carries one or morepredetermined control information bits.
 17. The user equipment accordingto claim 16, wherein the processing circuitry is configured to decodethe downlink control channel transmission using a predetermined subsetof a set of codewords.
 18. The user equipment according to claim 16,wherein control information bits are encodable into the downlink controlchannel transmission as any codeword from a set of possible codewordsthat each have the same number of control information bits, wherein theprocessing circuitry is configured to decode the downlink controlchannel transmission using the set of possible codewords or apredetermined subset of the set of possible codewords, dependingrespectively on whether channel conditions are above or below athreshold level.
 19. The user equipment according to claim 15, whereinthe downlink control channel transmission omits one or morepredetermined control information bits such that the downlink controlchannel transmission carries a reduced number of control informationbits.
 20. The user equipment according to claim 19, wherein theprocessing circuitry is configured to decode the downlink controlchannel transmission by applying rate matching in dependence on a totalnumber of the one or more omitted control information bits.
 21. Thenetwork node of claim 9, wherein the downlink control channeltransmission comprises a control information bit sequence of N bits,wherein the processing circuitry is configured to: in response todetermining that channel conditions are above the threshold level,encode N non-deterministic control information bits into the controlinformation bit sequence; and in response to determining that channelconditions are below the threshold level, encode X deterministic controlinformation bits and Y non-deterministic control information bits intothe control information bit sequence, where X≥1, Y≥1, and X+Y=N, whereinthe X deterministic control information bits are the one or morepredetermined control information bits whose one or more respectivevalues are known to the user equipment.
 22. The method of claim 1,wherein control information bits are encodable into the downlink controlchannel transmission as any codeword from a set of possible codewordsthat each have the same number of control information bits, wherein saidreduced number of control information bits is less than said same numberof control information bits, and wherein the method comprises encoding,into the downlink control channel transmission, said same number ofcontrol information bits as a codeword from the set of possiblecodewords or said reduced number of control information bits as aportion of a codeword from the set of possible codewords, dependingrespectively on whether channel conditions are above or below thethreshold level, wherein the portion of the codeword omits one or morecontrol information bits whose values are or are not predetermineddepending respectively on whether channel conditions are below or abovethe threshold level.
 23. The method of claim 5, wherein controlinformation bits are encodable into the downlink control channeltransmission as any codeword from a set of possible codewords that eachhave the same number of control information bits, wherein said decodingcomprises decoding the downlink control channel transmission using theset of possible codewords or a predetermined subset of the set ofpossible codewords, depending respectively on whether channel conditionsare above or below a threshold level.